Ma. Grela et al., HARNESSING EXCESS PHOTON ENERGY IN PHOTOINDUCED SURFACE ELECTRON-TRANSFER BETWEEN SALICYLATE AND ILLUMINATED TITANIUM-DIOXIDE NANOPARTICLES, JOURNAL OF PHYSICAL CHEMISTRY B, 101(51), 1997, pp. 10986-10989
Photons absorbed by nanocrystalline TiO2 particles at 254 nm are found
to be 7.7 times more efficient than those at 366 nm for driving the p
hotocatalytic oxidation of salicylate S in aerated aqueous sols. The o
ccurrence of this phenomenon is ascribed to the conjunction of (1) sho
rt diffusion times of photogenerated carriers to the surface of nanopa
rticles, a fact that allows chemical reaction to compete with energy r
elaxation, and (2) favorable donor E-0(S-/S-.) redox potential and int
erfacial reorganization energy lambda(R) values, which make electron-t
ransfer rates peak at energies inside the valence band of TiO2. Master
equation kinetic modeling shows that electron transfer from S into hy
perthermal valence band holes takes place at rates consistent with k(s
c) similar to 10(4) cm s(-1) at optimal exoergicity, if the excess ene
rgy is dissipated into the crystal lattice within a few picoseconds. H
ydroxyl ions as donors would require much slower thermalization rates.